737NG Dome Light Power

[allendc]

Hello
I understand that the 737 non-NG aircraft had the Dome light power connected to the 28v dc hot battery bus. Is it correct that the 737 Dome light power changed (28v dc bat bus sect 3) with the NG, now the battery switch must be on for the dome lamp to be turned on . Sorry for the simple question, but 9/11 closed the door to getting a lot of questions answered :-(

David
www.737FlightSim.com

[QAVION]

Anything connected to an aircraft hot battery bus does not require the battery switch to be ON to get power. "Hot" indicates that the bus is always powered. The chronometers, amongst other things, run off the hot battery... although this might be a bad example.... The clocks' internal time circuits usually run off the Hot Battery Bus, but the clocks' digital displays may run off other busses... so that the battery is not drained too quickly when the aircraft's generators are not running.

Rgds.
Q

[allendc]

Thanks QAVION for the reply on the bus issue, I just wanted to know if the Dome light on the 737NG was no longer on the Hot battery bus.

David

[QAVION]

Ooops... sorry, David... Misread your question :o

If someone doesn't come up with an answer sooner, I should be able to find out in a few days time.

Rgds.
Q.

[Stealth]

The white dome lights are powered by the Battery Bus. This is valid for all 737 variants.

[allendc]

Hi Stealth
So all 737's including the NG's white dome lights are connected to the hot battery bus? THis would allow the white dome lights to be turned on without the battery switch being on.

Thanks for the clarification

David

[Stealth]

It is the Battery Bus, not the Hot Battery Bus. This means that you need to turn the battery switch on. The only lights powered by the hot battery bus are the dim entry lights while the lavatory mirror lights are powered by the grnd service bus. These two sets of lights come on any time the external power is connected even though the battery switch is the off position. Cheers.

[QAVION]

I'd just like to confirm that, according to the Boeing Manuals, the 737NG does have the dome lights running off the Battery Bus (Battery Switch required). However, assuming we are talking about the two Dome lights at the back of the cockpit, the one to the left of the door has two bulbs. The larger of the two bulbs is powered by the Battery Bus under normal circumstances. The smaller bulb is powered by a rechargeable battery pack and is not normally illuminated. However, if the aircraft loses power and the emergency light switch is armed, this smaller bulb will be illuminated.

The battery pack, by the way, recharged by the Left Main DC Bus.

Hope this helps.
Rgds.
Q.

[allendc]

Thanks Q for the follow up!

I will wire the dome light switch so that it requires the battery switch to be on. Thank you for the additional info on the Dual Lamp Dome lamp.

David
www.737FlightSim.com